1. Field of the Invention
The present invention relates to a composition for depolymerization and removal of silicone residues.
2. Description of the Related Art
Various methods and compositions for removing or depolymerizing crosslinked or uncrosslinked silicones are known in the prior art. These include, for example: Swelling and removing with an organic or halogenated organic solvent; Swelling and removing with an amine such as diisopropylamine; Depolymerizing the polydimethylsiloxane with alkaline solutions of strong bases such as sodium hydroxide or potassium hydroxide as described, for example, in U.S. Pat. No. 2,710,843; Depolymerizing with short-chain or cyclic oligodiorganosiloxanes as described, for example, in DE 69122740 T2; Depolymerizing with aqueous solutions of strong acids such as alkylbenzenesulphonic acids, or sulphuric acid, hydrofluoric acid as described, for example, in JP 8250400 A; and Depolymerizing with a composition containing phosphonitrile halide compounds and short-chain oligodimethylsiloxanes of up to 7 Si-chain members as described, for example, in EP 0 884 368 A1.
The contrary use of cyclic or linear phosphonitrile halide compounds as chain growth addition or condensation polymerization catalyst to prepare long-chain polydimethylsiloxanes is long-established prior art, as is using the catalyst to equilibrate polydimethylsiloxanes as described in DE 196 07 264 A1.
U.S. Pat. No. 5,008,229 is directed to solutions of phosphonitrile chlorides in an organic solvent and the use of such compositions to accelerate the condensation and/or equilibration of hydroxyl-terminated diorganosiloxanes. Although improved results are obtained, an organic solvent such as ethyl acetate is used to facilitate the dissolution of the phosphonitrile chloride. DE 37 25 377 eliminates the use of an organic solvent by using a reaction product of a phosphorus-nitrogen chloride and of a cyclic diorganosiloxane, such as octamethylcyclotetrasiloxane, as a catalyst. Experience has shown, however, that reaction products of phosphorus-nitrogen chloride and octamethylcyclotetrasiloxane frequently have viscosities exceeding several thousand mPa·s (centipoises), making the materials less useful as catalysts for removing polydimethylsiloxane residues.
U.S. Pat. No. 7,232,770 B1 describes ammonium fluorides combined with amines in various solvents for removing silicone residues in the semiconductor sector.
The disadvantage of all previously known compositions for dissolving silicone is that they contain corrosive substances such as, for example, organic acids or alkalis which, when used to remove silicones from diverse substrates, lead to surface corrosion of metals.